1. Field of the Invention
The present invention relates to an articulated head for devices that are designed to carry out automatic positioning and orientation of a tool and are capable of performing industrial operations such as welding, machining, painting and so on, devices of this type being commonly designated by the term "industrial robots".
The "articulated head" or "robot wrist" is the articulated assembly which is mounted at the end of the robot arm and controls the orientation in space of the end effector, or end-of-arm tool.
The invention is more particularly concerned with articulated heads which have three axes of rotation and comprise three movable frames B.sub.1, B.sub.2, B.sub.3 mounted in succession along a longitudinal axis X--X. The first frame B.sub.1 is carried by the free end of the robot arm and is rotatable about a first axis A.sub.1 with respect to said arm. The second frame B.sub.2 is carried by the first frame B.sub.1 and is rotatable about a second axis A.sub.2 with respect to the first frame. The third frame B.sub.3 is carried by the second frame B.sub.2 and is rotatable about a third axis A.sub.3 with respect to the second frame. The function of said third frame is to support a tool which is positioned and oriented by the robot. The first axis A.sub.1 and the third axis A.sub.3 are longitudinal axes which coincide with the longitudinal axis X--X in the straight position of the articulated head. The second axis A.sub.2 is an intermediate transverse axis which is always perpendicular to the plane containing the axes A.sub.1 and A.sub.3.
2. Description of the Prior Art
Articulated heads having three axes of rotation of this type are already known. In order to drive these articulated heads and to produce movements of rotation about their three axes, provision is made for three hydraulic motors (or three electric reductiongear motors), at least two of which are housed within the movable frames of the articulated head.
This results in a heavy weight of moving parts and high moments of inertia which are not conducive to rapid movements and impair the accuracy of the articulated head.
In another known articulated head having three axes of rotation of this type, the three hydraulic rotary motors which control respectively each axis of the head are mounted within a control box carried by the robot arm but the transmission of motion between the motors and the axis of rotation controlled by these motors calls for highly complex kinematic chains which are costly and give rise to free relative movements or backlash.
The object of the present invention is to overcome the disadvantages of the known articulated heads by avoiding the need to mount heavy devices such as motors within the movable portions, by reducing the number of motors required and by simplifying the transmissions between the motors and the elements which are actuated by these motors.